Hydrothermal and NaOH-treated rice straw fibre: A potential lignocellulosic biosorbent material for removal of textile dyes from contaminated industrial wastewater.

This study assessed lignocellulosic rice straw fibres as a potential biosorbent for removing textile dyes from industrial effluents. Fibre extraction was performed via hydrothermal pre-treatment and pulping using dilute NaOH. The adsorption capacity of the biosorbent was tested on carcinogenic dyes, including malachite green (MG), methylene blue (MB), basic fuchsin (BF), and Congo red (CR). Characterization techniques included gravimetric composition analysis, Fourier-Transform Infrared (FTIR) Spectroscopy, High-Resolution X-ray diffraction (HR-XRD), Field Emission Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (FESEM-EDS), Brunauer-Emmett-Teller (BET) analysis and determination of the point of zero charge (p). It was found that the maximum removal efficiencies for cationic dyes (MG, MB, and BF) were 88.7 %, 87.5 %, and 82.87 %, respectively, under optimal conditions with a biosorbent dosage of 2 g L, a temperature of 28 °C, an initial dye concentration of 25 mg L, and a contact time of 120 min, with an optimal pH range of 4-7. Adsorption data followed the Langmuir isotherm model and pseudo-second-order kinetics. For the anionic dye CR, adsorption efficiency was limited to 22.2 %, achieved at pH 1 with a biosorbent dosage of 1 g L, a temperature of 28 °C, and a contact time of 90 min, conforming to the Temkin isotherm and pseudo-second-order kinetics. These findings demonstrate that rice straw fibres can serve as a cost-effective and eco-friendly biosorbent for cationic dye removal, offering a sustainable approach to mitigate textile dye pollution while addressing environmental concerns associated with rice straw residue burning, thereby adding value to this abundant agricultural byproduct.